(1) Field of the Invention
The present invention relates to isolating equipment from mechanical shock loads and more specifically to a method and apparatus for suspending an object or an equipment element in a fluid having substantially the same density as that of the object or equipment being isolated from shock loads.
(2) Description of the Prior Art
Shock to a component occurs when the component experiences a sudden deceleration. For example, when a component is dropped on a hard surface, the component experiences a deceleration of as much as 100G. This deceleration causes the weight of the object to increase by the same factor as the acceleration. In the case of circuit boards, a deceleration of this magnitude will destroy the bonding between the semiconductor chips and the circuit board.
Shock mounting avoids sudden variations in acceleration. This can be accomplished by applying the acceleration over a longer period of time such as by mounting the object on springs or other elastomers. This method effectively reduces the acceleration to values within an acceptable tolerance. However such a method requires a great deal of space in the mounting since the object must continue moving while the space defining structure is essentially stationary. Shock mounting can also be accomplished by providing an equal and opposite force to counter the shock.
Most prior art shock mounting systems isolate the equipment with a system of springs or dampers designed to limit the transmission of shocks from the mounting to the equipment.
Electronic components have been provided in a shock mounted case by means of a plurality of elastomeric mounting devices as shown for example in U.S. Pat. No. 4,937,806 issued to Babson et al. The prior art also teaches that mounting devices can be provided with a fluid filled cavity component such that these devices are suitable for use in isolating a vehicles engine from the vehicle body for example, see Kato et al U.S. Pat. No. 4,946,147. Hirazawa U.S. Pat. No. 5,009,404 also discloses a fluid filled elastic mount suitable for use as an engine mount.
Hamburgen et al. U.S. Pat. No. 5,130,889 discloses an integrated circuit protection system achieved by encapsulation of the component in a low viscosity liquid. The properly selected liquid protects the electrical connections while the use of a low viscosity liquid prevents stress on bonded wires caused by differing expansion coefficients. Nowhere does Hamburgen disclose any mechanical shock protection achieved by use of a fluid.
These prior art disclosures fail to show or to suggest a method or apparatus for providing a counterbalancing force on the object or component in order to shield the apparatus from mechanical shock loads.